The program to explore outer space has increasing requirements for electrical and thermal power. The conventional photovoltaic flat plate array may not be the optimal choice to supply the significantly larger quantities of power required by the next generation of space systems. One group of candidate replacement systems uses a curved reflector to focus the sun's energy onto a thermal absorber which transfers the energy to a working fluid that drives a heat engine/electric generator. This system promises higher overall efficiency with the disadvantage of increased complexity. The higher efficiency allows a smaller reflector aperture area for a given power output. This is a major advantage since it minimizes launch mass and low orbit aerodynamic drag. Low orbit aerodynamic drag is a major factor since it causes the orbit to decay, requiring a fuel-consuming rocket firing to re-achieve the original orbit. Therefore, the lower the required aperture, the lower the aerodynamic drag, the lower the mass of re-boost fuel that must be launched.
Light weight reflectors may be made by using a thin film as the reflective material. Of particular interest are those disclosures that form the film into a parabolic trough reflector. Simpson in U.S. Pat. No. 4,173,397 describes a thin film reflector sheet (22) stretched over wires (20) or rods (70) in a terrestrial environment protected from wind and rain. A major disadvantage of this invention is the lack of a smooth contour. The reflective areas between the wires or rods are planar (see FIG. 3); therefore, the reflector is an array of flat facets. This severely limits the optical concentration potential and therefore the overall efficiency potential of this device. Cohen in U.S. Pat. No. 4,184,482 describes a trough reflector for use under terrestrial roof rafters. The film (30) is stretched between two frames (32) which are held apart by a biasing spring (64) at the tubular member (24). The trough reflector assembly rotates about the tubular member (24) to track the sun. Bronstein in U.S. Pat. No. 4,293,192 describes a stretched film terrestrial trough reflector made of a reflector sheet (46) attached to forms (22) and (24) which are moved apart on a slideway (26) by a nut (38). Eaton in U.S. Pat. No. 4,493,313 describes a terrestrial trough collector using a stretched film (16) attached to parabolic end formers (18) which are forced apart by a spreader bar (12). All of the foregoing are directed to terrestrial use and are not adaptable to transportation into space or use in space. All of the foregoing have a rigid connection between the film or foil and the end formers such that the aperture area cannot be changed. Also, the end formers are rigid (rather than flexible) with respect to their curved (parabolic) shape, thereby creating a reflecting surface with a fixed focal length.